Hackers are often categorized into one of three groups...
White Hats...
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use their abilities for good, ethical, and legal purposes rather than bad, unethical, and criminal purposes
(Hoffman)
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disclose vulnerabilities to software vendors so they can be fixed
(Zetter)
Gray Hats...
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[don't] work for their own personal gain or to cause carnage, but they may technically commit crimes and do arguably unethical things
(Hoffman)
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sell or disclose their zero-day vulnerabilities not to criminals, but to governments—law enforcement agencies
(Zetter)
Black Hats...
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violate computer security for personal gain ... or for pure maliciousness
(Hoffman)
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steal data, such as passwords, email, intellectual property, credit card numbers or bank account credentials
(Zetter)
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sell information about the security holes to other criminals for them to use
(Zetter)